1. Field of the Invention
The present invention relates to an image processing device and a method thereof, and particularly relates to an image processing device and a method capable of measuring block noise intensity.
2. Description of the Related Art
It is known that, when encoded image data is decoded, noise is generated on a decoded image.
For example, when image data is compressed by compression methods such as a MPEG (Moving Picture Experts Group) system, an encoder divides the image data into rectangular blocks having the plural number of pixels and performs DCT (Discrete Cosine Transform) processing on the respective divided blocks.
Accordingly, when a decoder decodes image data which has been encoded by the MPEG system, level differences occur in pixel values between pixels at boundaries of respective blocks and block noise tends to occur in the decoded image data in principle.
A device for reducing or removing such block noise is generally realized by applying an LPF (Low Pass Filter) set to a known block size (for example, 8×8 pixel in the case of MPEG2) and a block boundary position to perform smoothing.
However, in the above simple method, there are problems that image information is lost due to blur or that block distortion newly occurs by applying the smoothing only at block boundaries.
The degree and intensity of block noise largely differ depending on image contents or conditions of the compressed encoding (for example, bit rate or quantization scale), therefore, there are problems that reduction is not effective in uniform block noise reduction processing when the block noise intensity is strong, or that adverse effects occur due to the loss of image information when the block noise is extremely low.
In order to avoid these problems, various devices and methods have been proposed until now.
However, an image signal on which scaling (resolution conversion/pixel-number conversion) has been performed on the side of a video output device such as a DVD (Digital Versatile Disk) player may be inputted on the side of a television receiver, therefore, it is necessary to comply with the size different from the block size (for example, 8×8 pixel) which is prescribed in the MPEG standards.
That is, part of such players include a function of performing scaling, therefore, even when a recorded signal is a signal having SD (Standard Definition) resolution such as 720×480 pixel, the signal may be outputted after converted into a signal having HD (High Definition) resolution of 1920×1080 pixel which is output resolution.
Additionally, even when the recorded signal is the HD signal, there exist a signal having 1440×1080 pixel resolution, and such signal may be outputted after converted into the HD resolution of 1920×1080 pixel.
As described above, quality of the digital-decoded signal largely differs due to effects by scaling and system difference, that is, whether input video is analog input or digital input (distortion is sometimes large and sometimes small).
The quality of the decoded image largely varies from low quality to high quality due to the difference of the encoding system and conditions at the time of compressed encoding such as bit rate as well as the image type (distortion tends to be increased at the time of active moving pictures or images having complicated image information even in the case of still images).
Accordingly, the noise reduction processing is efficiently applied to images ranging from low quality to high quality by estimating quality of the compression decoding image and by dynamically switching intensity of the noise reduction processing according to the estimated amount (refer to JP-A-2001-204029 (Patent Document 1) and JP-A-2007-281542 (Patent Document 2)).